The use of Code Division Multiple Access (CDMA) technology is increasing within wireless applications such as cellular and Personal Communication Systems (PCS). Its utilization will continue to be significant as CDMA technology is incorporated within new standards such as the third generation (3G) Direct Spreading (DS)—CDMA communication system currently being defined. In CDMA technologies, multiple users and/or multiple data streams of each user, which each transmit information on a different code channel, share the same frequency channel, hereinafter referred to as a carrier. Furthermore, CDMA transmitters may also utilize multiple carriers, and therefore, multiple CDMA carriers share the same power amplifier and other components within a particular transmitter. This sharing of carriers between users and/or the sharing of power amplifiers and other components between carriers cause compounded signals to have a high Peak to Average Power Ratio (PAPR) to be processed by said components. In the 3G DS-CDMA standards, multiple code channels share the same carrier within 3G mobile stations. Hence, similar to that for a base station, compounded signals with potentially high PAPR are input to the power amplifiers of 3G mobile stations.
In order to meet the out-of-band emissions requirements, a power amplifier and other components with this high PAPR input is required to provide good linearity in a large dynamic range. This makes the power amplifier one of the most expensive components within the communication system. The high PAPR also means that the power amplifier operation has low power efficiency. When considering the 3G DS-CDMA case, this low power efficiency reduces the battery life time for 3G mobile stations.
An apparatus is thus needed that can reduce the PAPR of CDMA signals input to power amplifiers. Such a device should reduce the peaks of the compounded input signals such that a less expensive power amplifier can be utilized with out-of-band emissions still being fully controlled. This device should also be relatively inexpensive and any degradation in terms of in-band signal quality should be within an acceptable range.